1. Field of the Invention
The present invention relates to processes for converting hydroxy carboxylic acids to useful products and, more particularly, to processes for decarboxylating carboxylic acids to produce peracids and other useful products. Specifically, the present invention relates to a process for decarboxylating polyfunctional carboxylic acids derived from biomass processing systems in order to produce useful products.
2. Description of the Prior Art
There are a wide variety of biomass processing systems which produce waste streams containing substantial portions of lactic acid and other hydroxy acids. Examples of such biomass processing systems include the pulp and paper industry utilizing alkaline chemical pulping methods such as the kraft and soda pulping processes. Cheese whey production also contains substantial amounts of lactic acid. During, for example, alkaline chemical pulping processes, the unavoidable degradation of polysaccharides leads to the production of saccharinic and lactic acids in substantial amounts, approximately 22% of the weight of the initial wood. In addition, saturated aliphatic carboxylic acids such as formic acid and acetic acid are also components of the liquor. These acids, as sodium salts, together with the dissolved lignin compose the spent liquor. Present day wood pulping processes burn these chemicals to recover the salts for reuse in the pulping process. The component having the largest fuel value of the spent liquor is the alkali lignin. Therefore, it would be highly desirable to find some other high value use for the hydroxy acids produced by these processes.
U.S. Pat. No. 4,303,488 describes a process for photoelectrochemically converting saturated carboxylic acids, such as acetic and propionic acids, to their corresponding alkanes, methane and ethane respectively. These resultant alkanes can be useful as low value gaseous fuels. Carboxylic acids (RCOOH) can also be electrolytically oxidized to alkanes (RR) or mixtures of alkanes, alkenes, esters and alcohols as exemplified in the text entitled Organic Electrochemistry, edited by M. M. Baizer and H. Lund, pages 435-462, 1985. The electrochemical behavior is a function of the electrode material, current density, solvent system, temperature and pressure. The behavior of polyfunctional carboxylic acids is a complex function of the above parameters and of the susceptibility of the functional group (other than the carboxylate) to the anodic potential.
It has long been known that lower aliphatic peracids can be produced from corresponding aldehydes. Examples of such production are illustrated in U.S. Pat. No. 2,804,473, issued Aug. 27, 1967, and in a text entitled, Industrial Organic Chemistry by Klaus Weissermel and Hans-Jurgen Arpe, pages 152 and 153, 1978. Alternative schemes for production of peracids involve the reaction of the carboxylic acids with hydrogen such as described in U.S. Pat. No. 4,101,570 issued in 1978. A further route to peracids is to oxidize volatile aldehydes to the corresponding carboxylic acids and then react these acids with hydrogen peroxide to produce lower aliphatic peracids. Peracids are very useful in the wood pulping industry as bleaching agents. Therefore, it would be highly desirable to produce peracids for use or reuse by the wood pulp industry.